94 ELEMENTARY PHYSIOLOGY. [iX. 



vigour and will extend over the limb until it 

 becomes almost as rigid as in 4. 



6. Mechanical Stimulation. 



Cut off the part of the nerve which has been 

 dipping in the salt solution; the chemical sti- 

 mulus being thus removed, the leg will become 

 flaccid again. 



Pinch the remaining nerve sharply with a pair 

 of forceps several times. At each pinch the 

 muscles of the leg will contract. The pinching 

 kills or injures the part of the nerve pinched; 

 hence it is necessary to begin at the cut end, 

 and work down towards the muscle. 

 The gastrocnemius muscle of this leg may be 

 used for 13, b. 



7. Curve of Single Muscular Contraction. 



Place the frog on a glass or porcelain plate ; on 

 the left side cut through the skin at the back of 

 the thigh and carry the skin cut half way up 

 the back. Lift up the urostyle and cut through 

 the muscles attached to its lower half, then 

 holding it well up cut through the muscles at- 

 tached to its upper half: it is as well to avoid 

 cutting the 10th nerve which runs along the 

 under surface of the muscles. Note the 7th, 8th, 

 9th and 10th nerves which unite to form the 

 sciatic; with strong scissors cut away the uro- 

 style and cut through the vertebral column 

 above the 7th nerve : lift up the lower piece of 

 the vertebral column and without injury to the 



